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On May 19, 2016, the United States Environmental Protection Agency (EPA) published new lifetime Health Advisories (HAs) for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) in drinking water. These new HAs replace the Provisional Health Advisories but remain legally unenforceable. The new HA levels are 0.07 ppb for PFOS and PFOA, either individually or combined, and the EPA concluded that these amounts will not result in adverse developmental effects to fetuses during pregnancy, or to breastfed infants. The prior provisional HA levels were 0.4 ppb for PFOA and 0.2 ppb for PFOS. The new HAs describe concentrations of drinking water contaminants at which health effects are not anticipated to occur over a lifetime, whereas the previous provisional HAs described exposures expected to occur over weeks to months.

Under the Unregulated Contaminant Monitoring Rule (UCMR), data are collected for contaminants suspected to be present in drinking water but have no health-based standards set under the Safe Drinking Water Act (SDWA). These data are then used by the EPA to help determine whether or not to regulate such contaminants. In a nationwide survey of 4,864 Public Water Systems (PWS) from 2013 to 2015, 0.9% (N=46) and 0.3% (N=13) of national public water systems exceeded the new HA for both chemicals. As this sample set represents only a small fraction of the total number of PWS in the United States, potentially hundreds of PWS may exceed the new HA.

The most interesting component of the new HAs, and the one exhibiting the most uncertainty, is the decision to provide a combined PFOA/PFOS HA. While these two chemicals are broadly in the same family of chemicals (perfluoroalkyl substances), PFOA is a perfluoroalkyl carboxylic acid, while PFOS is a perfluoroalkane sulfonic acid. While both include the perfluoroalkyl moiety, the difference in the functional group at the end of the chain imparts significantly different toxicological and chemical properties to the two substances.

EPA has promulgated a combined MCL before, most notably for the trihalomethanes (bromoform, chloroform, bromodichloromethane, and dibromochloromethane), disinfection products, found in virtually all water treated for drinking. In that case, though, utilizing a combined value made sense, since each chemical in that group shares similar toxicological and chemical properties. The similarities in the toxicokinetics among PFOA and PFOS are not as clear as that among the trihalomethanes, largely due to the lack of data, particularly for PFOS.